A head-up display (HUD) is a display surface that is substantially transparent and allows a user to look through the HUD and view information presented on the surface of the HUD, including the outside environment, without refocusing the user's eyes. Aircraft and motor vehicles typically utilize one type of HUD, called a fixed HUD, which allows the HUD to depict information relative to the orientation of the aircraft or vehicle. Another type of HUD is a moveable HUD, which is often mounted in a helmet or head-mounted visor. A moveable HUD can display similar elements, but corrects the positions of the image by sensing the movement of a person's head or body so that the images are still stable with respect to the outside world.
Military and commercial cockpits or flight decks have employed head-up displays for decades. HUD's have also migrated into many other applications including motorized vehicles. In aviation, with the exception of specific pilot tasks (e.g., targeting), HUD's are generally used to provide the pilot with flight instrument information such as airplane attitude, airspeed, altitude, flight path, and other information while the pilot's attention is focused outside of the aircraft. In a typical installation, a HUD projector projects an image onto an optical transparent “combiner”. The pilot or operator views the outside world through the transparent combiner, and the optical qualities of the combiner and the projector work together to focus the displayed image in a far field (e.g., focal point well outside the aircraft) as viewed by the pilot through the combiner, so that the pilot can view information and the outside world at the same time without re-focusing his or her eyes. The image appears to the operator to be projected onto the outside world. Aircraft also generally include primary flight displays installed on the main instrument panel in front of the pilot for use during head-down instrument flying.
Because of limitations inherent in existing HUD's, regulators do not usually approve HUD's as the sole source of aircraft display information for maintaining awareness of critical parameters and controlling the airplane. One drawback of existing HUD's is the difficulty to read data on a HUD under bright conditions, such as when the sun is near the horizon and appears in or near the HUD from the pilot's viewpoint. Additionally, when pilots are flying through or near brightly sunlit clouds, it may be difficult or impossible to read data presented on a HUD. For this reason, a HUD cannot be certified as the sole display on an aircraft for critical flight parameters such as attitude, altitude, airspeed, or heading.
Therefore, there exists a need for improved apparatuses and systems for providing head-up displays.